U.S. patent number 4,556,029 [Application Number 06/479,482] was granted by the patent office on 1985-12-03 for back-up system and method for engine coolant temperature sensor in electronic engine control system.
This patent grant is currently assigned to Nissan Motor Company, Limited. Invention is credited to Tatsuo Morita, Hiroshi Sanbuichi, Kunifumi Sawamoto, Satoshi Takizawa, Hiroshi Yamaguchi.
United States Patent |
4,556,029 |
Yamaguchi , et al. |
December 3, 1985 |
Back-up system and method for engine coolant temperature sensor in
electronic engine control system
Abstract
A back-up system for an engine coolant temperature sensor
detects deviation of the output of the temperature sensor from its
designed output range to produce a fault signal. In response to the
fault signal, an engine control system derives the engine coolant
temperature indirectly from other engine conditions. This
derivation is based on two facts: (1) the amount of fuel required
to start the engine is related to engine temperature, and (2) since
the calorific value of a given engine is essentially constant, the
rate of increase of engine temperature is related to the integrated
number of engine revolutions. Thus, when the engine is to be
started, engine temperature can be derived by gradually increasing
the fuel supply quantity from a minimal initial value until the
engine is able to start to determine the required fuel supply
quantity. Thereafter, the derived temperature value can be updated
as a function of total engine revolutions.
Inventors: |
Yamaguchi; Hiroshi (Yokosuka,
JP), Sawamoto; Kunifumi (Yokosuka, JP),
Sanbuichi; Hiroshi (Yokohama, JP), Morita; Tatsuo
(Yokohama, JP), Takizawa; Satoshi (Yokosuka,
JP) |
Assignee: |
Nissan Motor Company, Limited
(Yokohama, JP)
|
Family
ID: |
12949501 |
Appl.
No.: |
06/479,482 |
Filed: |
March 28, 1983 |
Foreign Application Priority Data
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|
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Apr 2, 1982 [JP] |
|
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57-53679 |
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Current U.S.
Class: |
123/41.15;
123/179.15; 123/479; 123/491 |
Current CPC
Class: |
F01P
11/16 (20130101); F02D 41/064 (20130101); G01K
7/42 (20130101); G01K 15/00 (20130101); F02D
41/222 (20130101); Y02T 10/40 (20130101) |
Current International
Class: |
F01P
11/16 (20060101); F02D 41/06 (20060101); F01P
11/14 (20060101); F02D 41/22 (20060101); F01P
011/16 (); F02D 005/00 () |
Field of
Search: |
;123/41.15,179L,479,491 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2237481 |
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Mar 1973 |
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DE |
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2949192 |
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Jun 1980 |
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DE |
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3024266 |
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Jan 1981 |
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DE |
|
3206028 |
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Apr 1982 |
|
DE |
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55-78131 |
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Jun 1980 |
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JP |
|
57-335 |
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Jan 1982 |
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JP |
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57-137632 |
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Aug 1982 |
|
JP |
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58-62342 |
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Apr 1983 |
|
JP |
|
Other References
Patent Abstracts of Japan, vol. 7, No. 153, (Jul. 5,
1983)..
|
Primary Examiner: Cuchlinski, Jr.; William A.
Attorney, Agent or Firm: Schwartz, Jeffery, Schwaab, Mack,
Blumenthal & Evans
Claims
What is claimed is:
1. A back-up system for an engine coolant temperature sensor in an
engine control system, comprising:
a fuel injection valve;
an engine coolant temperature sensor for detecting an engine
coolant temperature and producing an engine coolant temperature
signal indicative of the engine coolant temperature;
an engine speed sensor for detecting an engine revolution speed and
producing an engine speed signal indicative of the engine
speed;
monitoring means for detecting failure of the engine coolant
temperature sensor to produce a fault signal;
a starter switch for producing a starter signal while it is turned
ON for starting up the engine;
arithmetic means, responsive to turning ON of said starter switch,
for producing a fuel injection pulse to be fed to said fuel
injection valve having a pulsewidth gradually increased from a
predetermined initial pulsewidth, for measuring a period of time in
which said starter switch is maintained at ON position to assume
the engine coolant temperature on the basis of the measured period
of time, for determining a calorific value produced by the engine
revolution on the basis of the engine speed signal to determine an
increasing value of the engine coolant temperature after the engine
starting up, said arithmetic means producing an assumed engine
coolant temperature signal indicative of the assumed engine coolant
temperature.
2. The back-up system as set forth in claim 1, which further
comprises detector means for detecting the engine speed signal
value equal to or higher than a predetermined engine speed
threshold to produce an engine driving indicative signal, and
wherein said arithmetic means is responsive to the engine driving
indicative signal to determine the engine coolant temperature on
the basis of the period of time from when said starter switch is
turned ON to when said engine driving indicative signal is
produced.
3. The back-up system as set forth in claim 2, wherein said
arithmetic means determines said calorific value by integrating the
number of engine cycles on the basis of said engine speed
sensor.
4. The back-up system as set forth in claim 2, wherein said
arithmetic means compares said assumed engine coolant temperature
with a predetermined engine coolant temperature threshold to keep
the assumed engine coolant temperature constant when said assumed
engine coolant temperature becomes equal to or higher than said
engine coolant temperature threshold.
5. The back-up system as set forth in claim 4, wherein said
monitoring means comprises a comparator adapted to compare the
engine coolant temperature signal value with an upper first and a
lower second threshold, said comparator producing said fault signal
when said engine coolant temperature signal value is more than said
first threshold or is less than said second threshold.
6. The back-up system for an engine coolant temperature sensor in
an engine control system, comprising:
a fuel injection valve adapted to open in a period corresponding to
a fuel injection pulsewidth;
an engine coolant temperature sensor adapted to produce an engine
coolant temperature signal having a voltage corresponding to the
engine coolant temperature;
an engine revolution sensor for detecting the engine revolution to
produce an engine revolution indicative signal;
a starter switch adapted to produce a starter ON signal while said
starter switch is turned ON;
an engine speed detector adapted to detect the engine speed on the
basis of said engine revolution indicative signal to produce an
engine speed detector signal when the detected engine speed becomes
equal to or higher than a predetermined engine speed threshold;
an engine cranking period detector associated with said starter
switch and said engine speed detector for measuring a period from
the turning ON of said starter switch until the first of the
turning OFF of said starter switch and the occurrence of said
engine speed detector signal;
a fault monitor associated with said engine coolant temperature
sensor for detecting a condition in which the engine coolant
temperature signal voltage is outside of a predetermined range and
for producing a fault signal upon detecting said condition; and
arithmetic means, responsive to said fault signal, for performing a
back-up operation to assume the engine coolant temperature on the
basis of the engine operating condition, and for producing a fuel
injection control signal to control said fuel injection valve, said
arithmetic means determining a fuel injection pulsewidth which is
increased at a given rate corresponding to the cranking period from
a predetermined initial pulsewidth, assuming the engine coolant
temperature on the basis of the detected cranking period,
calculating a calorific value created by subsequent engine
revolution on the basis of said engine revolution indicative signal
to increase said assumed temperature in accordance with the
calculated calorific value and continuing to produce said fuel
injection control signal in accordance with said assumed engine
coolant temperature.
7. The back-up system as set forth in claim 6, wherein said
arithmetic means latches said assumed engine coolant temperature at
a constant value when said assumed engine coolant temperature
reaches a predetermined engine coolant temperature threshold.
8. The back-up system as set forth in claim 7, wherein said engine
coolant temperature threshold is set at a temperature which
corresponds to a set temperature of a thermostat in an engine
cooling system.
9. The back-up system as set forth in claim 7, wherein said
arithmetic means incorporates a memory storing said fuel injection
pulsewidth gradually increased during the engine cranking, the rate
of increase of said fuel injection pulsewidth having
characteristics determined on the basis of the required fuel
injection amount corresponding to the engine coolant temperature
for starting up the engine.
10. The back-up system as set forth in claim 9, wherein said
arithmetic means further includes a memory storing the engine
coolant temperature data to be read out in terms of the detected
engine cranking period.
11. The back-up system as set forth in claim 10, wherein said
arithmetic means integrates the number of said engine revolution
indicative signals to determine said created calorific value in the
engine revolution.
12. A back-up system for an engine coolant temperature sensor in an
engine control system, comprising:
a fuel injection valve for injecting fuel into the engine while a
fuel injection pulse is present;
an engine coolant temperature sensor for detecting an engine
coolant temperature and producing an engine coolant temperature
signal indicative of the engine coolant temperature;
an engine speed sensor for measuring engine revolution speed and
producing an engine speed signal indicative of the engine
speed;
monitoring means for detecting failure of the engine coolant
temperature sensor, and for producing a fault signal;
a starter switch for producing a starter signal while it is turned
ON to start the engine;
arithmetic means responsive to said starter signal for producing a
fuel injection pulse to be fed to said fuel injection valve having
a pulsewidth which gradually increases with a known, monotonic
behavior from a predetermined initial pulsewidth which corresponds
to the fuel injection quantity required to start the engine when
the engine coolant is at a first, relatively high temperature, for
measuring the period of time during which said starter signal is
produced, for deriving a substitute engine coolant temperature
value on the basis of the measured period of time, for determining
the rate of increase of the substitute engine coolant temperature
value in accordance with a calorific value of the engine and the
engine speed signal, said arithmetic means producing an assumed
engine coolant temperature signal indicative of the substitute
engine coolant temperature value in the presence of the fault
signal.
13. The back-up system as set forth in claim 12, which further
comprises detector means for detecting when the engine speed signal
value equal to or greater than a predetermined engine speed
threshold and for producing an engine-running indicative signal at
such times, and in which said arithmetic means is responsive to the
engine-running indicative signal to derive the substitute engine
coolant temperature from the period of time between the first
occurrence of said starter signal and said engine-running
indicative signal.
14. The back-up system as set forth in claim 13, wherein said
arithmetic means determines said rate of increase by integrating
the number of engine revolution cycles after production of said
engine-running indicative signal on the basis of said engine speed
sensor.
15. The back-up system as set forth in claim 13, wherein said
arithmetic means compares said assumed engine coolant temperature
with a predetermined engine coolant temperature threshold and holds
the assumed engine coolant temperature constant when said assumed
engine coolant temperature becomes equal to or greater than said
engine coolant temperature threshold.
16. The back-up system as set forth in claim 15, wherein said
monitoring means comprises a comparator adapted to compare the
engine coolant temperature signal value with an upper first and a
lower second threshold value, said comparator producing said fault
signal when said engine coolant temperature signal value is greater
than said first threshold or less than said second threshold.
17. The back-up system for an engine coolant temperature sensor in
an engine control system, comprising:
a fuel injection valve adapted to open to inject fuel into an
engine during a period corresponding to a fuel injection
pulsewidth;
an engine coolant temperature sensor adapted to produce an engine
coolant temperature signal having a voltage corresponding to the
engine coolant temperature;
an engine revolution sensor for detecting engine rotation and
producing an engine revolution indicative signal;
a starter switch adapted to produce a starter ON signal while it is
turned ON;
engine speed detector for calculating the engine speed on the basis
of said engine revolution indicative signal and producing an engine
speed detector signal when the calculated engine speed becomes
equal to or greater than a predetermined engine speed
threshold;
a engine cranking period detector associated with said starter
switch and said engine speed detector for measuring the cranking
period of time between the turning ON of said starter switch and
the first one of the turning OFF of said starter switch and the
occurrence of said engine speed detector signal; and
a fault monitor associated with said engine coolant temperature
sensor for detecting when the engine coolant temperature signal
voltage is outside of a predetermined range to produce a fault
signal; and
arithmetic means responsive to said fault signal for outputting a
fuel injection pulsewidth which is increased from a predetermined
initial pulsewidth at a given variable rate during said measured
period of time, for deriving a substitute coolant temperature on
the basis of said measured period, calculating the integral of the
engine revolution cycles on the basis of said engine revolution
indicative signal, increasing said substitute temperature in
accordance with the integrated engine cycle value, and adjusting
said fuel injection pulsewidth depending on said substitute engine
coolant temperature.
18. The back-up system as set forth in claim 17, wherein said
arithmetic means holds said substitute engine coolant temperature
to a constant value when said substitute engine coolant temperature
reaches a predetermined engine coolant temperature threshold.
19. The back-up system as set forth in claim 18, wherein said
engine coolant temperature threshold is chosen to be the
temperature to which a thermostat in an engine cooling system is
set.
20. The back-up system as set forth in claim 18, wherein said
arithmetic means incorporates a memory storing a table of said fuel
injection pulsewidth values arrayed in terms of said cranking
period so as to increase monotonically with cranking period, said
arithmetic means calculating said fuel injection pulsewidth during
engine cranking by reading the stored pulsewidth associated with
the currently measured cranking period value.
21. The back-up system as set forth in claim 20, wherein said
arithmetic means further includes a memory storing substitute
engine coolant temperature data arrayed in terms of final measured
cranking period.
22. A method of deriving the temperature of an internal combustion
engine, comprising the steps of:
(a) controlling the amount of fuel per engine revolution supplied
to the engine to an initial value in response to the closing of a
starter switch;
(b) increasing the amount of fuel as a known function of time until
the engine starts;
(c) measuring the length of time required to start the engine;
and
(d) calculating the engine temperature from the measured length of
time with reference to a known relationship between engine starting
time and engine temperature.
23. The method of claim 22, wherein said initial fuel supply value
is the amount of fuel required to start the engine when the engine
is at a known, relatively high temperature.
24. A method for backing up an engine coolant temperature sensor in
an engine control system, comprising the steps of:
(a) producing a fault signal upon detecting failure of the engine
coolant temperature sensor;
(b) in the presence of the fault signal, setting the amount of fuel
to be supplied to the engine per engine revolution to a minimal,
initial value in response to activation of a starter motor;
(c) increasing the fuel supply amount as a known function of time
until the engine starts;
(d) measuring the time required for the engine to start after
activation of the starter motor in order to derive the fuel supply
amount required to start the engine;
(e) deriving the engine coolant temperature at the time the engine
starts from the derived fuel amount with reference to a known
relationship between engine coolant temperature and fuel amount
required to start the engine;
(f) counting engine revolutions after the engine has started to
derive the integral of engine revolution;
(g) increasing the derived engine coolant temperature value in
accordance with the engine revolution count; and
(h) in the presence of the fault signal, adjusting the fuel supply
amount in accordance with the derived engine coolant
temperature.
25. The method of claim 24 wherein the output of the engine coolant
temperature sensor is designed to fall within a known voltage range
and said detecting failure of the engine coolant temperature sensor
comprises the steps of comparing the output of said sensor with
upper and lower values corresponding to the upper and lower limits
of said voltage range, respectively, and outputting the fault
signal when said output exceeds the upper value or falls below the
lower value.
26. A method of deriving the temperature of an internal combustion
engine comprising the steps of:
effecting fuel injection while the engine is being cranked by a
starter to inject a measured amount of fuel into a combustion
chamber of said engine, said measured amount of fuel being
increased at a given rate and at a given time;
detecting the time required to start said engine and further
detecting a final measured amount of fuel injected when the engine
starts;
determining the minimum amount of fuel per engine revolution
required to start the engine on the basis of the detected amount of
time required to start the engine and the final measured amount of
fuel; and
calculating the engine temperature from the determined required
fuel amount with reference to a known relationship between known
fuel amount and engine temperature.
27. The method of claim 26, further comprising the steps of:
(a) counting engine revolution cycles after the engine has been
started; and
(b) increasing the calculated engine temperature value in
accordance with the engine cycle count.
28. The method of claim 27 further comprising the step of halting
the increase of the calculated engine temperature value when the
engine temperature value reaches a predetermined upper limit.
Description
BACKGROUND OF THE INVENTION
The present invention relates generally to a fail-safe system in an
electronic engine control system, which allows the engine to
continue running even after one of the components of the electronic
engine control system fails. More particularly, the invention
relates to a back-up system for an engine coolant temperature
sensor, which is adapted to produce a substitute signal
approximately representative of the engine coolant temperature when
failure of the engine coolant temperature sensor is detected.
As is well known, an engine coolant temperature is an important and
fundamental control parameter in the electronic engine control
processes, such as fuel injection control, idling speed control,
fast idle control and so forth. Generally, the engine coolant
temperature is detected by an engine coolant temperature sensor
which produces a signal having a value corresponding to the engine
coolant temperature. The engine coolant temperature sensor is
installed in a water jacket surrounding the engine cylinders. For
example, when a thermistor-type engine coolant temperature sensor
is used, the output voltage of the sensor at -40.degree. C. is
about 4V and at 120.degree. C. is 1V. In electronic engine control
systems, the engine coolant temperature sensor output is fed to a
microcomputer via an analog-to-digital converter (hereafter
referred to as A/D converter).
If the engine coolant temperature sensor fails or the wiring
connecting the sensor to the microcomputer breaks, the values
received by the microcomputer from the engine coolant temperature
sensor will fall into an abnormal range. If left uncorrected, this
would result in failure of the engine control system.
Conventionally, the engine control system is provided with a
fail-safe or back-up system in order to continue control system
operation even when the engine coolant temperature sensor fails. In
the conventional system, the engine control system is responsive to
the abnormal values of the engine coolant temperature signal to set
the engine coolant temperature parameter to a predetermined value
which corresponds to a normal range of engine coolant temperature,
e.g. 80.degree. C. While this back-up system can keep the engine
control system operative, the control by the engine control system
may not accurately correspond to engine operating conditions. In
particular, under relatively cold engine conditions, such a back-up
system can degrade engine start-up characteristics and
drivability.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to provide a
back-up system for an engine coolant temperature sensor which is
able to more accurately approximate the engine coolant temperature
on the basis of at least one other engine operating parameter so
that an assumed substitute value varies in accordance with
variations in engine operating conditions.
Another object of the present invention is to ensure smooth engine
start-up even after failure of the engine temperature sensor while
simultaneously measuring engine temperature indirectly.
The system of the invention is incorporated in connection with and
in addition to the fuel control system of the engine. The method of
the invention is employed as an alternative to normal start-up fuel
control and in addition to normal operating fuel control when
engine temperature sensor operation is unreliable.
The system of the invention comprises a fuel injection valve, an
engine coolant temperature sensor, an engine speed sensor,
monitoring means for detecting failure of the engine temperature
sensor to produce a fault signal, a starter switch and arithmetic
means which in the presence of the fault signal produces a fuel
injection pulse to be outputted to the fuel injection valve and
which, after the starter switch is closed, has a pulsewidth which
increases monotonically in a known relationship with time until the
engine has been started, starting from an initial pulsewidth which
corresponds to the fuel quantity required to start the engine when
the engine coolant is at a known temperature, the arithmetic means
also measuring the period of time required to start the engine,
deriving an initial substitute engine temperature value on the
basis of the measured period of time and increasing the substitute
engine temperature value in accordance with the integrated number
of engine revolution cycles.
If the method of the invention, in response to the starter switch,
a fuel injection pulsewidth is assigned an initial value which
represents the minimal amount of fuel required to start a hot
engine and then while the starter motor cranks the engine, the fuel
injection pulsewidth is increased monotonically until the engine
starts. An initial value for the engine temperature can then be
derived from the period of time required to start the engine.
Thereafter, the engine temperature value is adjusted in accordance
with the integrated number of engine revolutions until the
temperature value reaches a preset upper limit.
The invention is based on the fact that the amount of fuel required
to start the engine varies with engine temperature. Thus, engine
temperature can be tested at engine start-up by gradually
increasing the fuel injection quantity until the engine starts.
Furthermore, since the calorific value of a given engine tends to
be constant, the heat output, and thus the rate of change of
temperature, of the engine can be derived simply from the integral
over time of the engine speed, i.e. the total number of engine
revolutions since the determination of the initial engine
temperature value.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be understood more fully from the
detailed description given herebelow and from the accompanying
drawings of the preferred embodiments of the invention, which,
however, should not be taken as limitative to the invention but for
elucidation and explanation only.
In the drawings:
FIG. 1 is a block diagram of a fuel injection control system
incorporating the first embodiment of an engine coolant temperature
sensor back-up system according to the present invention;
FIG. 2 is a circuit diagram of an engine coolant temperature sensor
monitor circuit of FIG. 1;
FIG. 3 shows the preferred characteristics of the fuel injection
pulsewidth t.sub.i in relation to cranking period t;
FIG. 4 shows the relationship between the engine coolant
temperature T.sub.w and the required fuel injection pulsewidth
t.sub.i corresponding to the engine coolant temperature;
FIG. 5 shows the relationship between the engine coolant
temperature T.sub.w and the cranking period t;
FIG. 6 is a flowchart of the engine coolant temperature sensor
back-up operation according to the first embodiment of the
invention;
FIG. 7 is a block diagram of a fuel injection control system
incorporating the second embodiment of the engine coolant
temperature sensor back-up system according to the present
invention; and
FIG. 8 is a timing diagram showing the relative timing and
pulsewidths of various signals.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings, particularly to FIG. 1, there is
illustrated the preferred embodiment of an engine coolant
temperature sensor back-up system according to the present
invention, which back-up system is associated with a control unit C
which consists predominantly of a microcomputer. A thermistor-type
engine coolant temperature sensor 1 is installed in an engine
coolant passage (not shown) in the engine cylinder block. The
engine coolant temperature sensor 1 is connected for output to an
analog-to-digital converter 2 via dividing resistors R.sub.1 and
R.sub.2 and is adapted to adjust the voltage at the junction A
thereof in accordance with the engine coolant temperature. The
analog-to-digital converter 2 produces a digital signal S.sub.t
indicative of the engine coolant temperature and feeds the engine
coolant temperature indicative digital signal S.sub.t to an
interface 8 in the control unit C.
The voltage at the junction A is also applied to an engine coolant
temperature sensor fault monitor circuit 9. The monitor circuit 9
monitors the temperature sensor output voltage and responds to an
abnormal range of sensor voltage to produce a HIGH-level fault
indicative signal S.sub.f and, otherwise, holds the fault
indicative signal S.sub.f at LOW-level. In practice, the monitor
circuit 9 causes the fault signal level to go HIGH when the sensor
voltage is not within a predetermined range, e.g. 0.5 V to 4.5 V.
The monitor circuit 9 is connected for output to a flag register 81
of the interface 8 of the control unit C.
The control unit C generally comprises a CPU 3, a memory unit 4 and
the interface 8. As is well known, the interface 8 feeds input data
to the CPU 3 via a data bus and outputs output data or output
signals to perform engine control operations. In the shown
embodiment, the control unit C is adapted to control fuel injection
amount by controlling the operation of a fuel injection valve 7.
The control unit C is also connected to an engine speed sensor 5
which produces an engine speed signal S.sub.N indicative of the
engine revolution speed, a starter switch 6 which is turned on
while the engine is cranking during start up, and an engine load
sensor 50 for producing an engine load signal S.sub.Q indicative of
the load condition on the engine.
In the fuel injection control operation, the control unit C
determines a basic fuel injection amount T.sub.p on the basis of
the value of the engine speed signal S.sub.N and the value of the
engine load signal S.sub.Q and corrects the fuel injection amount
by a correction coefficient determined on the basis of the value of
the engine coolant temperature indicative signal S.sub.t.
The fuel injection amount T.sub.i corrected by the engine coolant
temperature dependent correction coefficient may be further
corrected on the basis of various fuel injection control
parameters, such as acceleration enrichment, fuel-cut, transient
correction and so forth, according to well known procedures. For
example, U.S. Pat. No. 4,319,327 to Kazuhiro Higashiyama et al
discloses a Load Dependent Fuel Injection Control System for
determining the basic fuel injection amount on the basis of the
engine speed and engine load parameters and correcting the basic
fuel injection amount by a correction coefficient determined on the
basis of the engine speed and the engine load and an engine
temperature dependent correction coefficient. The disclosure of
U.S. Pat. No. 4,319,327 is herewith incorporated by reference for
disclosure purposes.
As shown in FIG. 2, the engine coolant temperature sensor fault
monitor circuit 9 comprises a pair of comparators 10 and 11, an
inverter 12 and an OR gate 13. As seen from FIG. 2, the engine
coolant temperature sensor 1 is connected to the negative input
terminal (-) of the comparator 10 and to the positive input
terminal (+) of the comparator 11. To the positive input terminal
(+) of the comparator 10, a reference voltage generator 10' is
connected to feed a reference signal S.sub.1 having a voltage
representative of a predetermined lower threshold, e.g. 0.5 V. On
the other hand, the comparator 11 is connected to a reference
voltage generator 11' to receive from the latter a reference signal
S.sub.2 having a voltage representative of a predetermined upper
threshold.
In this construction, as long as the voltage inputted to the
comparators 10 and 11 from the engine coolant temperature sensor
remains within a normal range defined by the upper and lower
threshold, the comparator 10 outputs a HIGH-level comparator signal
S.sub.3 which is inputted to the OR gate 13 as a LOW-level signal
via the inverter 12 and the comparator 11 outputs a LOW-level
comparator signal S.sub.4 to the OR gate. Therefore, as long as the
engine coolant temperature sensor output voltage is in the normal
range, the output of the OR gate which serves as the fault
indicative signal S.sub.f remains LOW. If the engine coolant
temperature sensor fails and thus the engine coolant temperature
sensor output drops below the lower threshold, the comparator 10
outputs a LOW-level comparator signal S.sub.3 so that a HIGH-level
signal is received by the OR gate 13 from the inverter 12. Thus,
the signal level of the fault indicative signal S.sub.f goes HIGH.
Similarly, when the engine coolant temperature sensor output level
exceeds the upper threshold, the signal level of the comparator 11
goes HIGH and so causes the fault indicative signal level to go
HIGH.
Preferably, a known delay circuit will be provided in the monitor
circuit 9 to provide a fixed delay before outputting the HIGH-level
fault indicative signal S.sub.f after the failure of the engine
coolant temperature sensor is detected so that the HIGH-level fault
indicative signal is outputted only while the output level of the
engine coolant temperature sensor remains outside of the normal
range for more than a predetermined period of time.
Returning to FIG. 1, the memory 3 includes a data memory 41, a
program memory 42 and a register 43. The input/output interface 8
includes a register 81 associated with a clock generator 82 which
produces a train of constant-period clock pulses S.sub.c. The
register 81 is also associated with the starter switch 6 to count
clock pulses S.sub.c while the starter switch is in the ON
position. The register 81 is, therefore, cleared in response to the
leading edge of the HIGH-level starter signal S.sub.s and is
latched in response to the trailing edge of the HIGH-level starter
signal S.sub.s. The data memory 41 comprises a random access memory
(RAM) for storing temporary values of fuel injection control
parameters. In addition, the data memory 41 stores fuel injection
pulsewidth data for the engine coolant temperature sensor back-up
operation. The fuel injection pulsewidth data may be stored in the
data memory in the form of a look-up table reflecting the
characteristics shown in FIG. 3. In FIG. 3, the fuel injection
pulsewidth t.sub.i (labelled "Ti" in the drawings) during engine
cranking is selected to increase with the cranking period t, i.e.
with elapsed time during cranking. In the engine coolant
temperature sensor back-up operation, the fuel injection pulsewidth
t.sub.i is set to a minimum value t.sub.i0 in response to closing
of the starter switch 6. The fuel injection pulsewidth t.sub.i is
increased thereafter in relation to the cranking period t as
illustrated in FIG. 3. The final fuel injection pulsewidth t.sub.i
may be latched either when the starter switch 6 is opened again or
when the engine speed N exceeds a predetermined engine speed
threshold N.sub.0 indicative of self-sustaining engine
operation.
The data memory 41 also stores engine coolant temperature data
which are read out in terms of the final fuel injection pulsewidth
t.sub.1. The final fuel injection pulsewidth t.sub.1 reflects the
engine coolant temperature at the time of cranking as shown in FIG.
4. In FIG. 4, the line D represents an upper limit of the fuel
injection pulsewidth t.sub.i for starting the engine corresponding
to a given engine coolant temperature and the line E represents a
lower limit. Therefore, the fuel injection pulsewidth t.sub.1 at
the end of engine cranking should be within the hatched range. As
apparent from FIG. 4, the final fuel injection pulsewidth t.sub.1
decreases as the engine coolant temperature T.sub.w rises and
reaches its minimum value at engine coolant temperatures above
about 60.degree. C. FIG. 5 shows the characteristics of variation
of the cranking period t in relation to the engine coolant
temperature. As set forth previously, the final fuel injection
pulsewidth t.sub.1 is a known function of the cranking period t as
illustrated in FIG. 3. Therefore, the engine coolant temperature
T.sub.w may be derived or approximated on the basis of the cranking
period t according to the characteristics of FIG. 5. The engine
coolant temperature data can thus be stored in the data memory 41
in the form of a look-up table accessed in terms of the cranking
period.
The program memory 42 stores a fuel injection control program and a
back-up program to be executed when failure of the engine coolant
temperature sensor is detected. The back-up program is shown in
FIG. 6 in the form of a flowchart. After starting the fuel
injection control program, the flag register 81 is checked in block
101. If the FLAG is "0" and thus the answer at the block 101 is NO,
the normal fuel injection control program is executed, as
represented by a block 102. On the other hand, if the FLAG is "1"
and thus failure of the engine coolant temperature sensor 1 is
detected, the starter switch position is checked at a block 103. If
the starter switch 6 is in the ON position and thus the engine is
cranking, the engine speed N is compared to a predetermined engine
speed threshold N.sub.0 at a block 104. If the engine speed is
lower than the engine speed threshold N.sub.0, the count value in
the register 82 of the input/output interface 8 is read out. As set
forth previously, the register value is representative of elapsed
time since the starter switch was turned ON. In other words, at the
block 105, the cranking period t is read out. Based on the cranking
period t, the data memory 41 holding the fuel injection pulsewidth
data t.sub.i is accessed to obtain the fuel injection pulsewidth
corresponding to the current cranking period value at a block 106.
Thereafter, the fuel injection pulsewidth data t.sub.i is
transferred to the register 43 in the memory 4, at a block 107. At
a block 108, the data memory 41 holding the engine coolant
temperature data is accessed to derive a substitute engine coolant
temperature value T.sub.w in terms of the cranking period t. The
assumed engine coolant temperature T.sub.w is transferred to the
register 43 at a block 109.
If the starter switch 6 is ON when checked at the block 103 and the
engine speed N is higher than the engine speed threshold N.sub.0
when checked at the block 104, then program execution jumps
directly to the block 108. In this case, the final fuel injection
pulsewidth t.sub.1 is used to derive T.sub.w in step 108.
On the other hand, if the starter switch 6 is OFF and thus the
answer at the block 103 is NO, the engine coolant temperatue
T.sub.w stored in the register 43 is incremented by a given amount
so as to increase at a given rate, at a block 110. The rate of
increase of the engine coolant temperature is proportional to the
calorific value of the engine provided that the engine coolant
temperature T.sub.w is lower than a set temperature of a thermostat
provided in the engine coolant circulation system so that engine
coolant circulation is not required. The calorific value determines
how much heat is generated by the engine in every engine
revolution. Therefore, the rate of increase of the assumed engine
coolant temperature is determined on the basis of the integrated
number of engine revolution cycle. To enable the back-up system to
calculate the rate of increase of the engine coolant temperature,
the register 82 in the input/output interface 8 is adapted to count
engine revolutions. To register value showing the integral number
of engine revolution cycles will be cleared when the ignition
switch of the engine is turned OFF. Thus, the increment to the
engine coolant temperature T.sub.w may be determined on the basis
of the integrated number of the engine revolution cycles and on the
calorific value of the given engine.
The incremented engine coolant temperature T.sub.w is compared to a
predetermined temperature threshold T.sub.ref, e.g. 80.degree. C.,
which is the set temperature of a thermostat provided in the engine
coolant circulation system, at a block 111. If the incremented
engine coolant temperature T.sub.w is less than the temperature
threshold T.sub.ref, the engine coolant temperature data in the
register 43 is replaced by the incremented engine coolant
temperature, at subsequent blocks 112 and 109. On the other hand,
if the incremented engine coolant temperature is equal to or
greater than the temperature threshold, the engine coolant
temperature data in the register 43 is latched at the temperature
corresponding to the temperature threshold, at subsequent blocks
113 and 109. This is because engine coolant circulation triggered
by the thermostat will tend to place an upper limit on engine
coolant temperature.
After the block 109, the engine coolant temperature sensor back-up
program ends and the assumed engine coolant temperature data is
used for engine control operations, not only to control the fuel
injection amount but also to control engine idling speed, exhaust
gas recirculation rate and so forth.
FIG. 7 shows the second embodiment of the engine coolant
temperature sensor back-up system as employed in a fuel injection
control system. As in the foregoing first embodiment, the engine
coolant temperature sensor 200 produces a sensor signal having a
voltage indicative of the engine coolant temperature. An engine
coolant temperature signal generator 204 receives the sensor signal
and produces a engine coolant temperature signal S.sub.t. The
sensor signal is also applied to the engine coolant temperature
sensor monitor circuit 202. The monitor circuit 202 has the same
circuitry as in the foregoing first embodiment and is adapted to
produce the HIGH-level fault signal S.sub.f when the sensor signal
voltage is out of the predetermined normal range.
A crank angle sensor 206 is adapted to produce a crank reference
signal C.sub.ref at every predetermined crank shaft angular
position e.g. 90.degree. or 120.degree., and a crank position
signal C.sub.pos at every predetermined angle, e.g. 1.degree. or
2.degree., of the crank shaft rotation. The crank position signal
C.sub.pos is fed to an engine speed counter 208 which is adapted to
detect the engine speed N on the basis of the crank position signal
to produce an engine speed signal S.sub.N having a value indicative
of the engine speed. The engine speed counter 208 is connected to a
comparator 210 to which a reference signal generator 209 is
connected. The reference signal generator 209 produces a reference
signal S.sub.N0 having a value indicative of the predetermined
engine speed threshold N.sub.0. The comparator 210 compares the
engine speed signal value N to the reference signal value N.sub.0
to produce a HIGH-level comparator signal when the engine speed
signal value is equal to or greater than the reference signal value
and otherwise to produce a LOW-level comparator signal.
The comparator 210 is connected to an engine coolant temperature
calculator 212 to output the comparator signal thereto. The coolant
temperature calculator 212 is also connected to a timer 216 which
is, in turn, connected to the starter switch 214. The timer 216
produces a timer signal to measure the cranking period of the
engine. For this purpose, the timer 216 is cleared every time the
starter switch 216 is turned ON and thus the HIGH-level starter
signal rises. The coolant temperature calculator 212 latches the
timer signal value when the comparator signal level goes HIGH or
when the starter switch is turned off. As set forth previously, the
coolant temperature calculator 212 derives an approximated engine
coolant temperature value T.sub.w on the basis of the latched
cranking period t according to the characteristics shown in FIG. 5.
The coolant temperature calculator 212 produces a signal indicative
of the assumed engine coolant temperature which is stored in a
memory 218.
An arithmetic circuit 222 is connected to receive the output of the
memory 218 via a switching circuit 220 which is, in turn, connected
to receive the output of the coolant temperature signal generator
204. The switching circuit 220 is also connected to receive the
output of the engine coolant temperature sensor monitor circuit 202
which controls which of the memory 218 and temperature signal
generator 204 is to be connected for output to the arithmetic
circuit 222. The engine load sensor 226, the engine speed counter
208, and the starter switch 214 are also connected to the
arithmetic circuit. In the presence of the HIGH-level fault signal
S.sub.f from the engine coolant temperature sensor monitor circuit
202, the arithmetic circuit 222 is responsive to actuation of the
starter switch 214 to produce a fuel injection pulse having a
predetermined initial pulsewidth t.sub.i0. As long as the starter
switch 214 remains in the ON position, the arithmetic circuit 222
increases the fuel injection pulsewidth t.sub.i according to the
characteristics illustrated in FIG. 3. The arithmetic circuit 222
is responsive to the opening of the starter switch 214, i.e., the
HIGH-level comparator signal from the comparator 210 to latch the
fuel injection pulsewidth t.sub.i at that time, i.e. at the end of
engine cranking.
After the engine has started, the coolant temperature calculator
212 receives an integrated engine revolution cycle number
indicative signal from an engine cycle integrating circuit 211
which is, in turn, connected to the engine speed counter 208 and is
adapted to integrate the engine revolution cycle number. Based on
the signal value from the engine cycle integrating circuit 211, the
coolant temperature calculator 212 increases the assumed engine
temperature T.sub.w according to the characteristics of FIG. 5. The
value stored in the memory 218 is replaced by the increased assumed
engine coolant temperature. As set forth previously in the first
embodiment, the assumed engine coolant temperature T.sub.w as
stored in the memory 218 may be held constant after the assumed
temperature value becomes equal to or greater than the
predetermined engine coolant temperature threshold, e.g. 80.degree.
C.
The arithmetic circuit 222 determines the fuel injection pulsewidth
on the basis of the engine load signal S.sub.Q from the engine load
sensor 226, the engine speed signal S.sub.N from the engine speed
counter 208 and one of engine coolant temperature-indicative
signals from the engine coolant temperature signal generator 204 or
the memory 218. The fuel injection control signal having the
determined pulsewidth t.sub.i is fed to a register 228 to be
temporarily stored. The register 228 feeds a register signal
indicative of the stored fuel injection pulsewidth t.sub.i to a
comparator 234. The comparator 234 is, in turn, connected to
receive the output of a counter 230 adapted to count clock pulses
from a clock generator 232. The counter 230 is also connected to a
reference pulse generator 224 to receive therefrom a reference
pulse for each cycle of engine revolution. The counter 230 is
cleared by the reference pulses from the reference pulse generator
224. The comparator 234 compares the register signal value and the
counter value and produces a HIGH-level comparator signal when the
counter value becomes equal to or greater than the register signal
value.
The comparator 234 is connected for output to the base of a
transistor 236 and so is able to turn the latter on with the
HIGH-level comparator signal. Therefore, the transistor 236 remains
OFF, i.e. nonconductive, as long as the comparator signal remains
LOW, in other words, as long as the counter value is less than the
register value. The fuel injection valve 238 is open to inject the
fuel while the transistor 236 remains OFF and is closed when the
transistor is turned ON by the HIGH-level comparator signal.
The relative timing of signals from reference pulse generator 224,
register 228, and counter 230, as well as those signals controlling
fuel injection valve 238, is shown in FIG. 8.
As set forth previously, the engine coolant temperature sensor
back-up system according to the present invention can produce a
back-up signal indicative of the assumed engine coolant temperature
which varies in accordance with the engine operating conditions. As
a result, engine control after failure of the engine coolant
temperature sensor can be more precise and engine starting
characteristics can be significantly improved, even when the engine
is relatively cold.
Therefore, the invention fulfills all of the objects and advantages
sought therefor.
Although the invention has been disclosed in relation to fuel
injection control, the assumed engine coolant temperature may be
used in other engine control processes such as engine idling speed
control, exhaust gas recirculation control and so forth. Therefore,
the invention should not be limited to the shown fuel injection
control but should be considered as applicable to any engine
control system.
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